Use of Rhizopus stolonifer (Ehrenberg) Vuillemin in methods for treating industrial wastewaters containing dyes

ABSTRACT

Use of a fungal biomass for treating industrial wastewaters containing at least one dye, wherein:
         i. the fungal biomass contains at least the fungal species  Rhizopus stolonifer  (Ehrenberg) Vuillemin;   ii. the fungal biomass absorbs the at least one dye, so as to obtain wastewater that is basically free of the at least one dye.

TECHNICAL FIELD OF THE INVENTION

The present invention relates in general to methods for treating industrial wastewaters containing dyes. More particularly, the present invention relates to the use of fungal species in methods for treating industrial wastewaters containing dyes.

TECHNICAL BACKGROUND OF THE INVENTION

Large amounts of dyes are used in various industrial fields, such as food, drug, cosmetic, textile and tanning fields (McMullan et al., 2001). It is estimated that the annual world production of dyes is above 700,000 tons, more than a half of which include dyes for textile fibers, 15% are dyes for other substrates such as leather and paper, 25% are organic pigments and the remaining portion is made up of dyes for particular uses (McMullan et al., 2001, Pearce et al., 2003).

Depending on molecule charge, dyes can be classed into anionic (acid), cationic (basic) and non-ionic dyes. As an alternative, depending on the chromophore group they can be classed into azo, anthraquinone, indigo, stilbene dyes etc., or depending on their applications. Azo and anthraquinone dyes represent the most widespread classes of dyes for industrial applications (Soares et al., 2001). Azo dyes are characterized by the presence of a double bond N═N and by other groups that are hard to degrade (Martins et al., 2001) and represent more than 50% of total production. Their fixing capacity is generally low and so more than 40% of the amount used gets into industrial waste, which has a clear color resulting therefrom, even after accurate purification treatments (O'Neill et al., 1999). Anthraquinone dyes represent the second class for industrial relevance and can be divided into dyes derived from indigo and from anthraquinone. They are prepared by successive introduction of the substituents on the pre-formed skeleton of anthraquinone.

Every year 5% to 10% of the world production of textile dyes is discharged into industrial wastewaters, which get in their turn into natural waterways where they can cause great problems for the environment and for living organisms (Yesilada et al., 2003). As a matter of fact, conventional methods for treating wastewaters are not sufficient to completely remove most of the dyes, which therefore tend to accumulate in the environment due to their complex molecular structure, designed on purpose for giving high stability to light, water and oxidizing agents (Fu and Viraraghavan, 2002a).

Dyes are toxic substances as shown by ETAD (1989) in a test on animals for 4,000 dyes. They can also have a carcinogenic and mutagenic action, due to the formation of aromatic amines when they are degraded under anaerobiosis from bacteria, as was shown in several researches on fishes, mice and other animals (Weisburger et al., 2002). Genotoxic and carcinogenic effects are also possible on men, on whom dyes cause at least short-term phenomena of contact and inhaling irritation (Yesilada et al., 2003).

When dyes get into surface water, indirect damages to ecosystems are likewise serious. As a matter of fact, gas solubility is compromised and above all water transparency properties are altered, which results in serious consequences for flora and fauna (Fu and Viraraghavan, 2002a). Lower penetration of sun rays causes indeed a reduction of oxygen concentration, which can be in its turn fatal for most water organisms (Yesilada et al., 2003).

Toxic substances contained in waste of industries using dyes should therefore be completely removed before being released into the environment (Knapp et al., 2001). Physical and chemical purification methods are not always applicable and/or effective and always involve high costs for firms (Fu and Viraraghavan, 2001, Robinson et al., 2001).

Chemical treatments exploiting oxidizing processes are among the most used methods, above all thanks to their easy application. Some of them, however, involve the use of chemical compounds that are noxious for men's health and/or for the environment such as the use of bleaching agents (Knapp et al., 2001). Among the most widespread treatments the following should be mentioned: treatment with H₂O₂ together with iron salts, with sodium hypochlorite, with ozone, photochemical and photocatalytic methods, electrochemical destruction (Robinson et al., 2001).

Physical methods based on the absorption of dyes into various abiotic matrices have proved to be effective in many cases. Decolourization by absorption is mainly based on ion exchange, which is affected by several factors such as the interaction between the dye and the type of substances used for absorption, temperature, pH, contact time, etc. Active carbons, peat, wood chips, filtration membranes are the most used absorbing agents. Absorption is often favored by the use of ultrasounds (Robinson et al., 2001, Crini, 2006).

A valid alternative to most traditional treatments of dyed wastewaters, characterized by low cost and low environmental impact, is the use of biologic systems, i.e. biomasses that are able to degrade toxic substances up to the mineralization thereof (biodegradation), or absorb them more or less passively on their cell structures (biosorption) (Banat et al., 1996).

Recently, several researches have shown that biosorption can be regarded as a valid alternative to chemical-physical methods and to microbial and/or enzymatic biodegradation. Such researches have pointed out the capacity of various microbial biomasses (bacteria, yeasts, fungi and algae) to absorb or accumulate dyes (Polman et al., 1996, Crini, 2006), and among the various types of biomass the fungal biomass has proved to be particularly suitable, even if the mechanisms regulating absorption have not yet been fully explained (Knapp et al., 2001, Crini, 2006).

In studies on biosorption with fungal biomasses, Mitosporic fungi and Zygomycetes, belonging to the genus Aspergillus, Penicillium, Myrothecium and Rhizopus, are mainly used. Only in some cases Basidiomycetes are used, since for these fungi the main decolourization mechanism is degradation and, according to Knapp et al. (2001), absorption occurs only in the initial stage of fungus-dyes interaction, which allows to create a strong contact between chromophores and degrading enzymes associated to the surface of hyphae.

Mechanisms regulating dye biosorption by the biomass seem to vary both as a function of the chemical structure of the dye and as a function of the specific chemical and structural composition of the biomass used. As a matter of fact, it was shown that some dyes have a particular affinity for particular species of organisms (Robinson et al., 2001).

Fu and Viraraghavan (2002b), working with biomasses of Aspergillus niger that had been deactivated, dried, pulverized and subjected to various chemical treatments, so as to selectively deactivate different chemical groups, have shown that dye biosorption preferably occurs on cell wall, where the main binding sites would be made up of amine and carboxyl groups. It should still be explained whether during biosorption processes the dye is bound only to the outer surface or whether it can also be carried, at least partially, into the hyphae (Polman and Breckenbridge, 1996; Brahimihorn et al., 1992).

With respect to traditional chemical-physical methods, biosorption has indubitable advantages such as a highly rapid treatment and the possibility of recovering absorbed dye for future use. Moreover, it can be carried out also with deactivated biomasses; this has huge advantages both thanks to the lower environmental impact and because it is not necessary to monitor the various factors affecting the growth of a living organism.

However, there are several factors that might affect biosorption yields, in particular growth substrate, pH, incubation temperature and initial dye concentration (Aksu and Tezer, 2000; Abd El Rahim et al., 2003, Aksu Z., 2005).

DESCRIPTION OF THE INVENTION

The invention aims at identifying/selecting fungal species to be used in methods for treating industrial wastewaters containing dyes.

According to the present invention, such aim is achieved thanks to the solution specifically disclosed in the following claims. The claims are an integral and substantial part of the technical teaching provided here with reference to the invention.

In particular, the invention relates to the use of the fungal species Rhizopus stolonifer (Ehrenberg) Vuillemin in a method for the biosorption of industrial dyes, e.g. of the dyeing or tanning industry.

SHORT DESCRIPTION OF THE FIGURE

FIG. 1. Absorbance spectrum of the simulated effluent containing the mix of 10 dyes at test beginning of the test (T0) and after 2, 6 and 24 hours of incubation with the deactivated biomass of Rhizopus stolonifer MUT 1515 pre-grown in the culture medium GN1. The hatched line refers to the wavelength at which the modification of the absorbance spectrum is more evident.

(check that in the figure the key of abscissa and ordinate is in Italian)

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described in detail with reference to some preferred embodiments, provided by way of mere non-limiting example.

In a particular and preferred embodiment of the present invention, the fungal biomass used includes the strain of Rhizopus stolonifer (Ehrenberg) Vuillemin MUT 1515, deposited at the DSMZ (Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH) Braunschweig, Germany, under access number DSMZ 18655 on Sep. 15, 2006.

The results obtained by the present inventors show that biomasses, both living and deactivated, of R. stolonifer MUT 1515 have high biosorption yields, both towards single dyes belonging to the main classes of industrial dyes (azo and anthraquinone dyes), towards a simulated wastewater containing ten dyes differing in chromophore group (azo, anthraquinone or phthalocyanine group and in chemical group (acid, reactive or direct group, and towards three effluent models designed to mime wastes produced during cotton or wool textile dyeing processes. The added value of the last result stems from the fact that model effluents were prepared using mixed commercially important industrial dyes, contain high concentration of salts and mimic the industrial wastewaters also for the pH values introducing real parameters that often bars the attainment of good biosorption yields according to Aksu (2005). Most works on biosorption published until today relate to the treatment of simulated wastewaters containing single dyes or maximum 2-3 dyes simultaneously, with total concentrations of about 200 ppm and almost never above 800 ppm (Aksu and Tezer, 2000). The concentrations of wastewaters used in the present study (up to 5,000 ppm) can therefore be regarded as very high and representative of actual industrial wastewaters.

The comparison with data available from scientific literature shows that the values of sorption capacity for R. stolonifer MUT 1515 obtained towards industrial dyes are comparable both with values disclosed in the scientific literature for other living or deactivated fungal biomasses (Fu and Viraraghavan, 2000; 2002a; O'Mahoney et al., 2002; Zhang et al., 2003; Aksu, 2005), and with theoretical values for fungus Rhizopus oryzae towards different industrial dyes (Aksu and Tezer, 2000; Aksu and Cagatay, 2006). Table 1 contains sorption capacities of living or deactivated biomasses of different fungal species disclosed in the scientific literature, among which the fungal strain R. stolonifer MUT 1515 according to the present invention.

TABLE 1 Sorption Fungal capacity species Biomass Dyes used (mg g⁻¹) Authors Aspergillus Deactivated Basic Blue 9 (50 ppm) Up to 18.5  Fu and niger Viraraghavan, 2000 Aspergillus Deactivated Congo Red (50 ppm) Up to 17.6  Fu and niger Basic Blue 9 (50 ppm) Viraraghavan, Acid Blue 29 (50 ppm) 2002b Disperse Red 1 (50 ppm) Penicillium Living Reactive Red 241 (100 ppm) 115-160 Zhang at al., oxalicum Reactive Blue 19 (100 ppm) 2003 Reactive Yellow 145 (100 ppm) Rhizopus Deactivated Reactive Orange 16  90-190 O'Mahoney et oryzae (250 ppm) al., 2002 Reactive Red 4 (250 ppm) Reactive Blue 19 (250 ppm) MIX (450 ppm) Rhizopus Deactivated Reactive Black 5 (800 ppm) Up to 500.7 Aksu and arrhizus = R Remazol turquoise Blue-G Up to 773   Tezer, 2000 oryzae (800 ppm) Aksu and Cagatay, 2006 Rhizopus Living Direct Red 80 (1,000 ppm) Up to 101.8 * stolonifer Reactive Blue 214 Up to 162.1 (1,000 ppm) Rhizopus Deactivated Direct Red 80 (5,000 ppm) Up to 221.4 * stolonifer Reactive Blue 214 Up to 506.7 (5,000 ppm) Up to 232.0 RBBR (5,000 ppm) Up to 519.2 Mix of 10 dyes (5,000 ppm)

Rhizopus stolonifer has never been referred to in the scientific literature as being able to remove dyes from simulated industrial wastewaters, either as living or as deactivated biomass. Conversely, a reference of this kind concerns another species of the same genus, Rhizopus arrhizus A. Fisch., synonym of Rhizopus oryzae Went & Prins. Geerl., studied by O'Mahoney et al. (2002), for its capacity to absorb dye solutions as deactivated biomass. Moreover, other species of the genus Rhizopus have been studied for their capacity to absorb other molecules: chlorinated pesticides, Penicillin G and various heavy metals (Aksu and Tunc, 2005; Cliff et al., 2003; Aksu and Tezer, 2000; Prakasham et al., 1999; Brady and Tobin, 1995).

The fast removal of dyes both from simulated wastewaters, and effluent models as shown in the tests carried out by the present inventors, and above all the excellent decolourization percentages already obtained after 2 hours of treatment, point out the industrial applicability of the biomasses of Rhizopus stolonifer MUT 1515.

The higher sorption capacities observed with deactivated biomasses, together with the absence of modification of the absorption spectrum during the decolourization treatment, support the hypothesis according to which biosorption is a process involving only passive chemical and/or physical mechanisms, independently from fungus metabolism. The use of deactivated biomasses is preferable with respect to the use of living organisms both for environmental and for safety reasons. Moreover, deactivated biomasses have important application advantages: they do not require a continuous introduction of nutrients, they are not affected by high levels of toxic compounds that are often present in wastewaters to be treated, and in some cases they can be regenerated and/or used for following treatment cycles (Aksu, 2005).

The results obtained by the present inventors suggest that the chemical structure of dyes can affect sorption yields. Differences in steric size and/or charge distribution can be the factors affecting the interaction between the binding sites on fungus wall and dye molecules. Such hypothesis is confirmed by the modification of the profile of the absorption spectrum for the wastewater containing the mix of dyes, which has been detected during the test. Such spectrum modification can be explained assuming that some dyes can be absorbed more or less easily by the biomass (FIG. 1).

In the tests discussed in the present application, biomasses pre-grown on different culture media have significantly different sorption capacities with respect to the same dye.

It is known that the culture medium can modify both the chemical structure and the structure of cell wall (Bartniki-Garcia and Nickerson, 1962; Farkas, 1980; Krystofova et al., 1998; El-Mougith et al., 1999; Hefnavy et al., 1999; Znidarsic et al, 1999; Nemcovic and Farkas, 2001) as well as colony morphology (Pessoni et al., 2005). According to Znidarsic et al. (1999) the amount and quality of carbon and nitrogen sources can affect the amount of structural compounds, such as chitin and chitosane, and of other chemical groups that are present in cell wall.

Description of Rhizopus stolonifer (Ehrenberg) Vuillemin

Description of the fungus grown on Malt Extract Agar at 25° C. Woolly colonies, white color, grayish brown color at maturity, very fast growing, often above 2 cm of height. Heterothallic species; blackish brown zygospores, verrucose, with unequal suspensors, diameter of (75)150-200 microns. Hyaline to brown stolons, carrying on their end highly ramified rhizoids and up to 7 sporangiophores (generally 3-4), with a length up to a 3-4 mm. Globous or subglobous sporangia, dark brown color at maturity and diameter of (50)150-360 microns. Globous or ovoidal columella, diameter of (40)70-160(250) microns. Sporangiospores of globous, ellipsoidal or more irregular, often polygonal shape, striated, with a size of (4)7-15×6-8(12) microns. Clamidospores absent in stolons, in some cases present in submerged hyphae. Optimal growth temperature 25-26° C., minimum 5° C., maximum 32-33° C.

Materials and Methods

The isolate of Rhizopus stolonifer (Ehrenberg) Vuillemin MUT 1515 (deposited at DSMZ under access number 18655 on Sep. 15, 2006) is kept at Mycotheca Universitatis Taurinensis (MUT, Università di Torino, Dipartimento di Biologia Vegetale) as colony in active growth, on Agar Malt medium at a temperature of 4° C. and in the form of freeze-dried mycelium cryopreserved at a temperature of −80° C.

Tested Dyes and Preparation of Simulated Wastewaters and Effluent Models

Simulated Wastewaters

Biosorption tests have been carried out using 9 industrial textile dyes (Clariant Italia S.p.a.) and the model dye RBBR (Remazol, Brilliant Blue, Sigma-Aldrich, St. Luis, Mo.). The chemical-physical properties and, if available, the structural formula of the 10 dyes are listed in Table 2.

For each dye a stock solution at a concentration of 20,000 ppm has been prepared by dissolving the dye powder in distilled water. Such solutions have been sterilized by filtration (disposable cellulose acetate filters with pores having a diameter of 0.2 μm—Schleicher & Schuell GmbH, Dassel, Germany) and stored at 4° C. till the preparation of the simulated wastewaters.

Since in industrial dyeing processes reactive dyes are released into wastewaters in hydrolyzed form, the stock solutions of dyes B41, B49, B214, R243 and RBBR have been hydrolyzed by means of a 2-hour treatment at 80° C. with a solution of 0.1 M Na₂CO₃, and then neutralized with a solution of 1N HCl.

For biosorption tests with living biomasses the following simulated wastewaters have been used:

-   -   saline solution (9 g 11 NaCl) containing the industrial direct         azo dye R80 at concentrations of 200 and 1,000 ppm;     -   saline solution (9 g l⁻¹ NaCl) containing the industrial         reactive azo dye B214 at concentrations of 200 and 1,000 ppm.

For biosorption tests with deactivated biomasses the following simulated wastewaters have been used:

-   -   saline solution (9 g l⁻¹ NaCl) containing the industrial direct         azo dye R80 at concentrations of 1,000 and 5,000 ppm;     -   saline solution (9 g l⁻¹ NaCl) containing the industrial         reactive azo dye B214 at concentrations of 1,000 and 5,000 ppm.     -   saline solution (9 g l⁻¹ NaCl) containing the anthraquinone type         dye RBBR at concentrations of 1,000 and 5,000 ppm;     -   saline solution (9 g l⁻¹ NaCl) containing all ten dyes at a         final concentration of 5,000 ppm (mix).         Effluent Models

Three effluent models designed to mime wastes produced during cotton or wool dyeing processes were prepared using mixed industrial dyes at high concentrations. The effluent models were developed by partners of the EC FP6 Project SOPHIED (NMP2-CT-2004-505899) and used under the permission of the SOPHIED Consortium.

The industrial dyes used in these wastewater models were selected because of representative of the most structural dye types, commercially important and with a wide range of applications across the textile industries and were purchased from Town End (Leeds) plc. The chemical-physical properties and the structural formula of the 10 dyes are listed in Table 3. In addition to the dyes, these effluent models mimic the industrial ones also for the presence of different salts, often in high concentrations, and for the pH values.

The first wastewater (R1) contained a mix of 3 acid dyes (300 ppm in total), and has an ionic strength of 4.23·10⁻² and pH 5. The second wastewater (R2) contained a mix of 4 reactive dyes previously hydrolized (5000 ppm total), and has an ionic strength of 1.26·10⁻¹ and pH 10. The third wastewater (R3) contained a mix of 3 direct dyes (3000 ppm total) and has an ionic strength of 1.48 and pH 9. The exact composition of the 3 effluent models is listed in table 4. All the mimed effluents were sterilized by tindalization (three 1 hour cycles at 60° C. with 24 hr interval between cycles at room temperature).

Preparation of Fungal Cultures and Production of Biomass

The reproductive propagules have been taken from colonies in active growth aged 7 days, and suspensions have been prepared at the known concentration of 2.5·10⁵ conidia ml⁻¹ in sterile deionized water using a hemocytometer (Bürker's chamber). One ml of such suspension has been inoculated into 500 ml flasks containing 250 ml of culture medium. The following culture media have been used for producing the biomasses:

Culture medium GN1

glucose 20 g l⁻¹

ammonium tartrate 1 g l⁻¹

KH₂PO₄ 2 g l⁻¹

MgSO₄.7H₂O 0.5 g l⁻¹

CaCl₂.2H₂O 0.1 g l⁻¹

10 ml of a mineral solution containing: 5 mg l⁻¹ MnSO₄.5H₂O, 10 mg l⁻¹ NaCl, 1 mg l⁻¹ FeSO₄.7H₂O, 1 mg l⁻¹ CoCl₂.6H₂O, 1 mg l⁻¹ ZnSO₄.7H₂O, 0.1 mg l⁻¹ CuSO₄.5H₂O, 0.1 mg l⁻¹ AlK(SO₄)₂, 0.1 mg l⁻¹ H₃BO₃, 0.1 mg l⁻¹ NaMoO₄.2H₂O.

Culture medium GN4

glucose 20 g l⁻¹

ammonium tartrate 4 g l⁻¹

KH₂PO₄ 2 g l⁻¹

MgSO₄.7H₂O 0.5 g l⁻¹

CaCl₂.2H₂O 0.1 g l⁻¹

10 ml of a mineral solution containing: 5 mg l⁻¹ MnSO₄.5H₂O, 10 mg l⁻¹ NaCl, 1 mg l⁻¹ FeSO₄.7H₂O, 1 mg l⁻¹ CoCl₂.6H₂O, 1 mg l⁻¹ ZnSO₄.7H₂O, 0.1 mg l⁻¹ CuSO₄.5H₂O, 0.1 mg l⁻¹ AlK(SO₄)₂, 0.1 mg l⁻¹ H₃BO₃, 0.1 mg l⁻¹ NaMoO₄.2H₂O.

Culture medium EQ

glucose 20 g l⁻¹

ammonium tartrate 2 g l⁻¹

KH₂PO₄ 2 g l⁻¹

MgSO₄.7H₂O 0.5 g l⁻¹

CaCl₂.2H₂O 0.1 g l⁻¹

10 ml of a mineral solution containing: 5 mg l⁻¹ MnSO₄.5H₂O, 10 mg l⁻¹ NaCl, 1 mg l⁻¹ FeSO₄.7H₂O, 1 mg l⁻¹ CoCl₂.6H₂O, 1 mg l⁻¹ ZnSO₄.7H₂O, 0.1 mg l⁻¹ CuSO₄.5H₂O, 0.1 mg l⁻¹ AlK(SO₄)₂, 0.1 mg l⁻¹ H₃BO₃, 0.1 mg l⁻¹ NaMoO₄.2H₂O.

Incubation has been carried out under stirring at 110 rpm and at a temperature of 30° C. (thermostatic planetary stirrer Minitron Infors, Bottmingen, CH). After 7-8 days of incubation the biomasses have been taken from the culture medium by filtration, using a metal sieve with pores having a diameter of 150 μm, and have been rinsed several times with saline solution (9 g l⁻¹ NaCl) so as to remove residues of culture medium that might have interfered with following test stages.

The biomasses have been divided into two parts: one part has been kept alive, the other one has been deactivated, and both parts have been used in the following biosorption tests.

TABLE 2 Common Chromophore Chemical name Trade name C.I. name group group λ_(max) (nm) B113* Nylosan navy blue N-RBL acid blue 113 azo acid 541 → P 187 B214 Drimaren navy blue X-GN CDG reactive blue 214 azo reactive 607 B225 Nylosan blue F-2RFL P 160 acid blue 225 anthraquinone acid 590-626 B41 Drimaren turquoise X-B CDG reactive blue 41 phthalocyanine reactive 616-666 B49* Drimaren blue P-3RLN GR reactive blue 49 anthraquinone reactive 586-625 → B81* Solar blue G P 280 direct blue 81 azo direct 577 → R111* Nylosan scarlet F-3GL 130 acid red 111 azo acid 499 → R243 Drimaren red X-6BN CDG reactive red 243 azo reactive 517 R80* Solar red BA P 150 direct red 80 azo direct 540 → RBBR* Remazol brilliant blue R reactive blue 19 anthraquinone reactive 593 → Common name Chemical structure B113*

B214 B225 B41 B49*

B81*

R111*

R243 R80*

RBBR*

*Dyes whose chemical structure is shown in the right column.

TABLE 3 Acrony- Chromo- Chemical mus C.I. name phore class Chemical structure ABk194 Acid black 194 Azoic (1:2 Cr complex) Acid

ABk210 Acid black 210 Trisazoic Acid

AY194 Acid yellow 194 Azoic (1:2 Co complex) Acid

ABu62 Acid blue 62 Anthra- quinonic Acid

AR266 Acid red 266 Azoic Acid

AY49 Acid Yellow 49 Mono- azoic Acid

DrBu71 Direct blue 71 Trisazoic Direct

DrR80 Direct red 80 Polyazoic Direct

DrY106 Direct Yellow 106 Stilbenic Direct

RBk5 Reactive black 5 Disazoic Reactive

Rbu222 Reactive blue 222 Disazoic Reactive

RR195 Reactive red 195 Mono- azoic Reactive

RY145 Reactive Yellow 145 Mono- azoic Reactive

TABLE 4 Dyes and Concentration Effluent model salts g l⁻¹ pH Acid bath for Abu 62 0.10 5 wool AY 49 0.10 (R1) AR 266 0.10 Na₂SO₄ 2.00 Reactive dye Rbu 222 1.25 10 bath for cotton RR195 1.25 (R2) RY145 1.25 Rbk 5 1.25 Na₂SO₄ 70.00 Direct dye bath DrBu 71 1.00 9 for cotton DrR 80 1.00 (R3) DrY 106 1.00 NaCl 5.00 Deactivation of Biomass

The biomasses have been placed in saline solution (9 g l⁻¹ NaCl) and deactivated by sterilization in autoclave at a temperature of 120° C. for 30 minutes. After such treatment the biomasses have been rinsed several times with saline solution.

Biosorption Tests

Living and deactivated biomasses have been divided into 3 g aliquots (living weight) and incubated in 50 ml flasks containing 30 ml of simulated wastewater. 3 repetitions have been prepared for each test.

Incubation has been carried out under stirring at 110 rpm and at a temperature of 30° C. (thermostatic planetary stirrer Minitron Infors, Bottmingen, CH). After 2, 6 and 24 hours of incubation 300 μl of simulated wastewater have been taken for each sample and centrifuged at 14,000 rpm for five minutes, so as to remove biomass fragments that might have interfered with following spectrophotometric measures.

By means of a spectrophotometer Amersham Biosciences (Fairfield, Conn.), the wastewater absorption spectrum in the visible has been acquired for each sample (λ=360 nm to λ=790 nm).

In the case of simulated wastewaters, the decolourization percentage (DP), expressed as percentage of removed dye, has been calculated for each sample according to the following formula: DP=100[(Abs₀−Abs_(t))/Abs₀] wherein Abs₀ is absorbance at time 0 and Abs_(t) is absorbance at time t, at the maximum wavelength in the visible (λ_(max)) for each dye (Table 2). Mix absorbance has been measured at a wavelength of 588 nm, corresponding to the maximum absorption in the visible.

In the case of effluent models, the DP values were calculated as the extent of decrease of the spectrum area from 360 nm to 790 nm, respect to that of the abiotic control.

Samples of simulated wastewaters and model effluents without biomass have been used as abiotic controls and for detecting the presence, if any, of bleaching phenomena not related to biosorption, such as photodegradation and complexing.

At the end of the test the biomasses have been filtered on filter paper (Whatman type 1), placed in an oven and dried at a temperature of 65° C. for 24 hours, then weighed so as to obtain the dry weight for each biomass. It has thus been possible to calculate sorption capacity (SC) according to the following formula: SC=mg of removed dye/g of biomass_((dry weight))

When complete decolourization is achieved, SC is underrated, since removed dye is only part of what the biomass might have removed.

The significance of the differences (p≦0.05) between DP and SC values has been calculated by means of Mann-Whitney's non-parametric test (SYSTAT 10 for Windows, SPSS Inc., 2000).

Results

Biosorption Tests with Living Biomass

Decolourization percentages (averages and standard deviations of 3 repetitions) of simulated wastewaters containing dyes R80, B214 at a concentration of 200 ppm, after 2, 6 and 24 hours of incubation with living biomasses of Rhizopus stolonifer MUT 1515 pre-grown in EQ, GN1 and GN4, are shown in Table 5.

TABLE 5 Culture Decolourization percentage (%) Dye medium 2 hours 6 hours 24 hours R80 EQ 99.8 ± 0.1 99.8 ± 0.1 99.9 ± 0.0 GN1 99.7 ± 0.1 99.7 ± 0.1 99.9 ± 0.0 GN4 97.2 ± 3.2 99.5 ± 0.1 99.8 ± 0.1 B214 EQ 100.0 ± 0.0  99.2 ± 0.7 99.8 ± 0.2 GN1 97.7 ± 0.3 98.8 ± 0.5 99.4 ± 0.3 GN4 99.6 ± 0.2 99.7 ± 0.3 99.1 ± 0.2

Table 6 shows decolourization percentages of simulated wastewaters containing dyes R80, B214 at a concentration of 1,000 ppm, after 2, 6 and 24 hours of incubation with living biomasses of Rhizopus stolonifer MUT 1515 pre-grown in EQ, GN1 and GN4. The values contained therein represent averages±standard deviations of three repetitions.

TABLE 6 Culture Decolourization percentage (%) Dye medium 2 hours 6 hours 24 hours R80 EQ 39.5 ± 5.8 46.0 ± 0.8 64.5 ± 2.8 GN1 33.4 ± 0.6 43.7 ± 1.3 61.9 ± 0.9 GN4 30.8 ± 1.7 39.0 ± 1.1 49.1 ± 1.3 B214 EQ 98.0 ± 0.2 98.9 ± 0.1 GN1 94.2 ± 1.1 97.6 ± 0.3 GN4 91.0 ± 0.2 96.5 ± 0.1

With simulated wastewaters at a concentration of 200 ppm an almost total decolourization has been obtained after 24 hours of treatment; both dyes have been removed with percentages that are always above 97% already in the first two hours of treatment (Table 5).

At a concentration of 1,000 ppm, the dye B214 has been removed more effectively than R80 with decolourization percentages, after 24 hours, that are always above 96%. Moreover, already after 2 hours of treatment the decolourization percentages observed were in all cases above 91%. The dye R80 has been the most difficult to remove from the simulated wastewater, reaching after 24 hours of treatment decolourization percentages that are almost always above 60% (except for biomasses pre-grown on GN4) (Table 6).

The monitoring of absorption spectra of simulated wastewaters before and after treatment shows that decolourization occurs only by means of biosorption (no biodegradation takes place), since the spectrum profile does not change although dye concentration sinks.

Table 7 shows sorption capacities of biomasses of Rhizopus stolonifer MUT 1515 pre-grown in EQ, GN1 and GN4 towards simulated wastewaters containing dyes R80 and B214 at a concentration of 1,000 ppm. The values contained therein represent the averages of three repetitions±standard deviations; different letters indicate significant differences (p≦0.05) among SCs of biomasses pre-grown on the different media with the same simulated wastewater.

TABLE 7 Sorption capacity (mg of dye g⁻¹ of biomass) Dye EQ GN1 GN4 R80 93.9 ± 3.4^(A) 103.9 ± 2.3^(B) 101.8 ± 3.6^(B)  B214 96.6 ± 1.4^(A) 126.2 ± 9.3^(B) 162.1 ± 28.4^(B) Different letters refer to significant differences (p ≦ 0.05) among SCs of biomasses pre-grown in different culture media for the same simulated wastewater.

With both simulated wastewaters the living biomasses of R. stolonifer MUT 1515 pre-grown on culture media GN1 and GN4 have proved to be the most suitable for removing dyes, achieving SC values of 103.9 mg g⁻¹ (R80, GN1) to 162.1 mg g⁻¹ (B214, GN4).

Biosorption Tests with Deactivated Biomass

Simulated Wastewaters

Decolourization percentages (averages and standard deviations of 3 repetitions) of simulated wastewaters containing dyes R80, B214 at a concentration of 1,000 ppm, after 2, 6 and 24 hours of treatment with deactivated biomasses of R. stolonifer MUT 15159 pre-grown in EQ, GN1 and GN4, are shown in Table 8.

TABLE 8 Culture Decolourization percentage (%) Dye medium 2 hours 6 hours 24 hours R80 EQ 87.2 ± 5.5 99.5 ± 0.2 100.0 ± 0.0 GN1 83.7 ± 0.1 99.5 ± 0.1 100.0 ± 0.0 GN4 65.1 ± 4.0 85.5 ± 3.5 100.0 ± 0.0 B214 EQ 97.5 ± 0.1 97.9 ± 0.2  98.2 ± 0.1 GN1 95.1 ± 1.1 97.0 ± 0.4  97.5 ± 0.1 GN4 97.2 ± 0.5 98.2 ± 0.2  98.3 ± 0.6 RBBR EQ 87.2 ± 5.5 99.5 ± 0.2 100.0 ± 0.0

Table 9 shows decolourization percentages of simulated wastewaters containing dyes R80, B214 at a concentration of 5,000 ppm, after 2, 6 and 24 ore of incubation with deactivated biomasses of Rhizopus stolonifer MUT 1515 pre-grown in EQ, GN1 and GN4. The values contained therein represent averages±standard deviations of three repetitions.

TABLE 9 Culture Decolourization percentage (%) Dye medium 2 hours 6 hours 24 hours R80 EQ 25.5 ± 3.5 26.1 ± 3.4 35.3 ± 1.0 GN1 17.9 ± 2.6 19.1 ± 3.1 26.9 ± 1.0 GN4 16.6 ± 3.9 21.5 ± 1.3 30.5 ± 1.1 B214 EQ 39.8 ± 3.5 51.2 ± 1.4 57.5 ± 5.6 GN1 25.8 ± 5.5 44.2 ± 4.6 49.3 ± 1.3 GN4 24.5 ± 4.0 41.9 ± 5.8 51.8 ± 3.7 RBBR EQ 63.4 ± 1.4 61.3 ± 1.8 59.6 ± 2.6 Mix EQ 35.4 ± 0.7 49.7 ± 4.9 64.1 ± 1.8 GN1 39.0 ± 0.8 52.1 ± 1.8 66.4 ± 0.9 GN4 32.5 ± 4.7 50.2 ± 1.5 66.4 ± 0.2

At a concentration of 1,000 ppm and after 24 hours of treatment, dyes R80 and RBBR have been almost completely removed from the biomass pre-grown in all culture media, with high decolourization percentages already after 2 hours. The dye B214 has been removed with decolourization percentages that are always above 95% and 97.5% after 2 and 24 hours, respectively (Table 8).

As for wastewaters containing single dyes or the mix of 10 dyes at 5,000 ppm, good decolourization yields have been achieved after 24 hours of treatment for dyes B214, RBBR and for the mix, with decolourization percentages of 49.3% (B214) and 66.4% (mix). The dye R80 has been removed less effectively (decolourization percentages below 35.3%) (Table 9).

As for living biomasses, during biosorption with deactivated biomasses no change in spectrum form has been observed for single dyes (R80, B214 and RBBR). Conversely, a change in the profile of the absorption spectrum has been observed for the wastewater containing the dye mix, in particular at a wavelength of about 560 nm. Such change can be explained assuming that some dyes may be absorbed by the biomass more or less easily (FIG. 1).

Table 10 contains sorption capacity values of deactivated biomasses of Rhizopus stolonifer MUT 1515 (averages±standard deviations of 3 repetitions) pre-grown in EQ, GN1 and GN4 towards simulated wastewaters containing dyes R80, B214 and RBBR as well as the mix of 10 dyes at a concentration of 5,000 ppm. SC values obtained with dyes at 1,000 ppm are not shown therein since decolourization percentage was so high (close to 100%) to prevent a correct calculation of this parameter.

TABLE 10 Sorption capacity (mg of dye g⁻¹ of biomass) Dye EQ GN1 GN4 R80 221.4 ± 24.4^(Aa) 179.9 ± 19.6^(Aa) 193.5 ± 15.9^(Aa) B214 506.7 ± 33.7^(Ba) 379.0 ± 37.4^(B) ^(b) 418.5 ± 53.7^(B) ^(b) RBBR 232.0 ± 23.1^(A) Mix 519.2 ± 37.1^(Ba) 494.1 ± 54.6^(Ca) 507.2 ± 66.9^(Ba) ^(a,b,c)refer to significant differences (p ≦ 0.05) among values of sorption capacity obtained with biomasses pre-grown in different culture media for the same simulated wastewater. ^(A,B,C)refer to significant differences (p ≦ 0.05) among values of sorption capacity towards different simulated wastewaters in the same culture medium.

A comparison of the three different culture media used for producing the biomass (EQ, GN1 and GN4) points out that the sorption capacity of Rhizopus stolonifer MUT 1515 does not vary significantly towards the dye R80 and the mix, whereas it is significantly higher when the biomass is grown in EQ.

Dyes R80 and RBBR have been the hardest to remove, independently from the medium used for biomass pre-growth.

Effluent Models

Table 11 shows decolourization percentages (average±standard deviations of 3 replicates) of effluent models, after 2, 6 and 24 hours of incubation with the biomass of Rhizopus stolonifer MUT 1515 pre-grown in EQ.

TABLE 11 Culture Decolourization percentage (%) Effluent medium 2 hours 6 hours 24 hours R1 EQ 89.1 ± 7.3^(A) 93.7 ± 1.2^(A) 92.3 ± 2.9^(A) R2 EQ 61.2 ± 3.0^(A) 61.7 ± 2.0^(A) 59.4 ± 1.7^(A) R3 EQ 35.3 ± 3.1^(A) 51.1 ± 3.2^(B) 84.0 ± 1.9^(C) ^(A,B,C)refer to significant differences (p ≦ 0.05) among values of decolourization percentage at different incubation time.

Substantial decolourization of R1 was achieved with DP values higher than 92% within 24 hours; more than 96% of the DP obtained at the end of the experiment was obtained within 2 hours.

The DP values of R2 were higher than 59% after 24 hours. No significant differences were observed between the DP values at 2, 6 and 24 hours for both R1 and R2, demonstrating that for these effluents the sorption equilibrium was reached.

The DP value of R3 was higher than 84% after 24 hours. In comparison to the other simulated effluents, lower percentage of the total decolourization (42%) was attained within 2 hours and significant differences were observed among the DP values at 2, 6 and 24 hours.

Obviously, details and embodiments can be widely varied with respect to what has been here described and shown, although without leaving the protection scope of the present invention as defined in the appended claims.

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1. Use of a fungal biomass for treating industrial wastewaters containing at least one dye, wherein: i. the fungal biomass contains at least the fungal species Rhizopus stolonifer (Ehrenberg) Vuillemin MUT 1515, DSMZ No. 18655; ii. the fungal biomass absorbs the at least one dye, so as to obtain wastewater that is basically free of the at least one dye.
 2. The use according to claim 1, characterized in that the at least one dye belongs to the class of azo or anthraquinone dyes, phthalocyanine dyes.
 3. The use according to claim 1, characterized in that the at least one dye contains a chromophore group chosen from the group comprising azo groups, anthraquinone groups, phthalocyanine groups, indigo groups and stilbene groups.
 4. The use according to claim 1, characterized in that the fungal biomass is living.
 5. The use according to claim 1, characterized in that the fungal biomass is deactivated, preferably by sterilization.
 6. The use according to claim 1, characterized in that the fungal biomass is grown in a culture medium containing a carbon source.
 7. The use according to claim 6, characterized in that the culture medium containing a carbon source is selected among starch, glucose, sucrose or mixtures thereof.
 8. The use according to claim 7, characterized in that the fungal biomass is grown in a culture medium containing glucose.
 9. The use according to claim 6, characterized in that the fungal biomass is grown in a culture medium further containing an ammonium salt, preferably ammonium tartrate.
 10. A method for treating industrial wastewaters containing at least one dye, including the following steps: a. preparing a fungal biomass comprising at least the fungal species Rhizopus stolonifer (Ehrenberg) Vuillemin MUT 1515, DSMZ 18; b. contacting the fungal biomass with the industrial wastewater for a sufficient lapse of time so as to enable the absorption of the at least one dye by the fungal biomass, thus obtaining wastewater that is basically free of the at least one dye.
 11. The method according to claim 10, characterized in that the fungal biomass is grown in a culture medium containing a carbon source.
 12. The method according to claim 11, characterized in that the culture medium containing a carbon source is selected among starch, glucose, sucrose or mixtures thereof.
 13. The method according to claim 12, characterized in that the culture medium contains glucose.
 14. The method according to claim 11, characterized in that the culture medium further contains an ammonium salt, preferably ammonium tartrate, preferably an amount of 2 g l⁻¹.
 15. The method according to claim 11, characterized in that the culture medium further contains at least a salt of K, Mg, Ca, Na, Mn, Fe, Co, Zn, Cu, Al, B and Mo.
 16. The method according to claim 10, characterized in that the fungal biomass is separated from the culture medium before the fungal biomass is contacted with the industrial wastewater to be treated.
 17. The method according to claim 10, characterized in that the fungal biomass is deactivated by means of chemical or physical treatment before it is contacted with the industrial wastewater to be treated.
 18. The method according to claim 17, characterized in that the fungal biomass is deactivated by sterilization. 